The Digital Millennium Copyright Act of 1998 has been the source of both controversy and consternation since it became law 15 years ago. Because of the DMCA, it became illegal to defeat the encryption on a DVD you purchased so you could watch a movie on your Linux computer.

It became illegal to make a binary copy of a movie so you could watch it on your iPad. Now, because the Librarian of Congress has decided it to be this way, it’s now illegal to unlock phones purchased on or after Jan. 26.

No doubt you’re asking yourself several questions. First, how is it that the DMCA has anything to do with phones? Second, why does the Librarian of Congress have anything to do with whether phone unlocking is illegal? We could go on from there.

Basically the way it works is this. Every three years the Librarian of Congress, which was made the responsible party for determining exemptions to the DMCA issues a report in situations in which the law doesn’t apply.

For the last six years, the Librarian has allowed phone unlocking. That exemption was removed last year, and it takes effect on Jan. 26. But as you might expect, this is anything but straightforward. You can read it for yourself right here, but be aware that the part you’re interested in starts halfway down the page, past the aviation stuff.

First, even if you can’t unlock your phone, you can still jailbreak it. The reasoning is that you should be allowed to enable your cell phone to use legally acquired software, even if the phone manufacturer or the carrier doesn’t like it. But just in case you’re tempted, you can jailbreak a phone, but not a tablet. I realize that this makes no sense.

But this doesn’t mean an end to unlocked phones. It’s still perfectly legal to buy a phone that’s already unlocked, which is one reason that the Librarian of Congress decided it’s OK to outlaw unlocking. It’s also legal to unlock your phone if the carrier says you can. So that means that if you call AT&T and ask for an unlock code, AT&T can give it to you and you can unlock your phone legally. It’s worth noting that AT&T announced last year that it would provide unlocking information for customers whose contracts have expired.

T-Mobile already has a policy of unlocking phones on request after you’ve had them for 90 days. With Sprint and Verizon Wireless, the question is still up in the air. But with those CDMA phones, the primary reason people want them unlocked is so they can use them overseas where CDMA service is rare. For the most part, those companies don’t lock the GSM functions of their phones.

What this really means boils down to two things. It puts a crimp in the operations of commercial unlocking operations that buy large quantities of no-contract phones, unlock them and then sell them (usually outside the United States) as unlocked phones. It also puts somewhat of a crimp in T-Mobile’s efforts to get AT&T customers to switch. After all, once an AT&T customer’s contract has expired, AT&T has said it will unlock their phones.

This also apparently means that you can’t unlock tablets just as you can’t jailbreak them, however, the biggest population of tablets is iPads, and they’re already unlocked. Even the iPads that are sold by AT&T, Verizon and Sprint that have SIM cards (which are required for LTE) aren’t locked. So if you want to put in a foreign SIM when you travel, you can.

So why has the Librarian of Congress made this rather inconsistent ruling on unlocked phones? The way the LoC reads the DMCA, unlocking the phone circumvents the technological protection of the software in the device. How this came to be interpreted this way is a mystery, since the only purpose for unlocking a phone is to change carriers, not to steal the software.

What’s even more of a mystery, given the reasoning of the LoC is that jail breaking is OK, even though that effectively unlocks the phone. But perhaps the most mysterious of all is how the DMCA came to be applied to phone unlocking. Or at least it’s a mystery until you realize that the major carriers have been lobbying the Librarian of Congress for years.

The bottom line for all of this is that basically very little has changed for individual owners of mobile phones. These individual owners already depended on their carrier’s help in unlocking or they bought unlocked phones. Even in cases where a person has unlocked a phone without the carrier’s permission, nothing has happened. There’s no reported instance in which a carrier has sued a customer for unlocking a phone.

But this does illustrate how a vast, complex bill such as the DMCA can have an impact on tech users far beyond anything that was ever intended. And unfortunately, because the DMCA is so vast and complex, it’s a safe bet that wireless companies will be working to think up new ways to make your use of the devices you buy more annoying. In the meantime, if you want your phone unlocked, go for it. Just be aware that somewhere in Washington, D.C., there’s a librarian who will cast a disapproving eye in your direction.